This invention relates generally to drives for machine tools having large movable assemblies mounted on fixed carriages, and more particularly concerns drives which can rapidly start and rapidly and precisely halt such assembly motion.
In modern manufacturing shops, many machine tools include large fixed carriages upon which move large, heavy, high-inertia assemblies. For example, core and mold machines are often found in metal foundries for making sand cores and molds used in casting operations for metal molding. These sand shell core and mold manufacturing machines include a fixed carriage, and a large, heavy, heated die or core box mounted for rotation or oscillation upon the carriage. During machine operation, a mixture of sand and resin binder is introduced, as by blowing into the die. To spread the sand and resin evenly about the interior surfaces of the die, and to provide a high quality mold product, the die is rotated or oscillated as the sand and resin are being injected.
When the casting mold or core has been fully formed within the machine, die movement is stopped, a die door is opened, and the finished sand core or mold is removed. When die oscillation stops, it is essential that the die come to rest at a precise location so that the door can be opened and closed without interference with other machine parts.
The oscillating core box or die and movable assembly which carries the die on a machine carriage can be quite heavy--they can weigh on the order of 1000 to 2000 pounds. Heretofore, this movable assembly has been oscillated on the machine carriage by a drive including an electric motor operating through a worm gear speed reducer. A small brake at the motor blind end assists in halting die movement and in retaining the die in the desired position for die door opening.
However, practical experience with the machine and its drive has shown that after a period of service, the drive parts wear sufficiently so that precise die positioning for door opening becomes an increasing problem. Adjustment and readjustment of this drive and die-locating mechanism may be required two or three times during a working day or shift. The resulting machine down time can thus be a matter of concern and frustration to the machine operator and a matter of considerable expense to the machine owner.
It is therefore the general object of the present invention to provide a drive for heavy machine tools which overcomes the foregoing difficulties.
More specifically, it is an object of the present invention to provide a machine tool drive having good starting and stopping torque characteristics for starting machine operation quickly, and for stopping machine motion quickly and precisely.
A related object is to provide such a machine drive which is reliable and rugged in operation, and which provides a long service life with minimal adjustment and repairs. A further object is to provide such a drive which is not greatly subject to drive part wear.
Another object is to provide such a machine drive which is compact in its overall shape and size to permit the drive to be located at a convenient position in and upon the machine.
Still another object is to provide such a machine drive which can be offered at a commercially attractive price. An ancillary object is to provide such a drive which requires no expensive adapters or interconnectors between a motor and a brake unit.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.